The present invention relates generally to a distributed antenna system for use in mobile communications, and more particularly to a distributed antenna system wherein a plurality of antenna units are widely distributed in a service area and controlled by a centralized controller. In addition, the present invention relates to a method of controlling the distributed antenna system.
As a method of constructing base stations for mobile communications with use of cellular phones, there has been proposed a method wherein a plurality of antenna units each comprising an antenna and a transmission/reception amplifier unit are provided in a communication service area and controlled by a centralized controller in a centralized manner.
FIG. 1 shows a conventional distributed antenna system. In the conventional distributed antenna system, as shown in FIG. 1, antenna units 101, 102 and 103 are distributed and controlled by a centralized controller 100. Cables or optical fibers are used to connect the centralized controller 100 and antenna units 101, 102 and 103. The centralized controller 100 performs such a control that radio frequencies are assigned for information transmission between the antenna unit 101, 102, 103 and terminals 104 in an associated zone Z1, Z2 and Z3, and transmission/reception signals are modulated/demodulated. The processing of signals for the antenna units 101, 102 and 103 is performed independently. With this structure, the control can be effected by the centralized controller 100 in a centralized manner. If a great number of antenna sections are provided, the cost for installation can advantageously be reduced.
In the conventional distributed antenna system, however, no countermeasure has been taken for a multipath, phasing, etc. which are problems at all times in mobile communication of cellular phones, etc. Specifically, in a case where only one antenna unit can be accessed by the terminal side within the service area in the distributed antenna system as shown in FIG. 1, communication may be interrupted on a time-axis due to multi-path, phasing, etc. or shifting of terminals.
As has been described above, in the conventional distributed antenna system, no countermeasure is taken for multi-path or phasing which are problems in mobile communications, and the reliability of communication is low.